1. Field of the Invention
The present invention relates to a cross link multiplexer bus.
2. Background Art
Ethernet protocol is a popular technology used to implement Local Area Networks (LANs), and was originally developed in the late 1970s. In 1985, Ethernet was adopted by the Standards Board of the Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) as IEEE Std 802.3® entitled “Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications”. Since its initial release, IEEE Std 802.3 has been amended on several occasions to capture the benefits of advances in networking technologies and to drive the development of future advancements. For example, the IEEE-SA has approved an amendment for “Media Access Control (MAC) Parameters, Physical Layers, and Management Parameters for 10 Gb/s Operation” to IEEE Std 802.3. The amended standard is designated IEEE Std 802.3ae™. The technology it supports is commonly referred to as “10 Gigabit Ethernet” and it represents a substantial increase in the speed at which signals can be communicated over an Ethernet medium.
IEEE Std 802.3ae introduced Clause 48 entitled “Physical Coding Sublayer (PCS) and Physical Medium Attachment (PMA) Sublayer, Type 10GBASE-X.” 10GBASE-X refers to a family of 10 Gb/s Physical Layer implementations. FIG. 1 shows the relationships among the 10GBASE-X sublayers and other layers in the CSMA/CD LAN hierarchy. The 10 Gigabit Media Independent Interface (XGMII) protocol is used to communicate between the Reconciliation Sublayer (RS) and the PCS. XGMII characters are converted to code groups by the PCS. The code groups are communicated in a parallel format to the medium by the Media Dependent Interface (MDI), which is used to communicate between the Physical Medium Dependent (PMD) sublayer and the medium. Optionally, XGMII Extender Sublayers (XGXSs) can be used to extend the operational distance of the XGMII. A Data Terminal Equipment (DTE) XGXS can be coupled to the RS and a Physical (PHY) XGXS can coupled to the Physical layer. The 10 Gigabit Attachment Unit Interface (XAUI) protocol can be used to communicate between the DTE XGXS and the PHY XGXS.
Manufacturers of network devices can implement the requirements of the Ethernet processes in any manner they choose. They are also free to include other processes so long as these do not conflict with the standard. Network devices that meet these criteria are said to be compliant with the standard. For example, Cisco Systems, Inc. developed the Converged Data Link (CDL) protocol, which can increase the distance over which signals are communicated over an Ethernet medium.
A signal is conveyed by a bus. Traditionally, a bus is configured to convey a signal received at a destination port directly to an origin port. Systems having more than two ports can use a cross link multiplexer at each destination port to route the signal directly to a desired origin port. Such a bus is referred to as a cross link multiplexer bus. The signal is often represented as a series of characters, which in turn can be represented by data bits and control bits. What is needed is a cross link multiplexer bus configured so that the bits of a character remain synchronized as they are conveyed in parallel by interconnects within the cross link multiplexer bus.